Polarizing plate, fabrication method thereof, and display device using the same

ABSTRACT

A polarizing plate, a fabrication method thereof, and a display device using the same are provided. The polarizing plate includes a polarizing element, a first adhesive layer formed on one surface of the polarizing element, a second adhesive layer formed on the other surface of the polarizing element, a protective film attached to an upper portion of the first adhesive layer, a bonding layer attached to a lower portion of the second adhesive layer, and a luminance enhancement film attached to the bonding layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.2011-0011993 filed on Feb. 10, 2011, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polarizing plate used in a displaydevice and a fabrication method thereof, and more particularly, to apolarizing plate having an enhanced light leakage which occurs as thepolarizing plate is bent when a luminance enhancement film is laminatedthereon, and a fabrication method thereof.

2. Description of the Related Art

In general, a polarizing plate is formed by attaching atriacetylcellulose (TAC) film as a protective film to a polarizer inwhich polyvinyl alcohol (PVA)-based molecule chains are oriented in acertain direction and which have a structure containing an iodine-basedcompound or a dichroic polarizing material. Here, in general, thepolarizer and the protective film are attached by a water-based adhesiveconfigured as a PVA-based aqueous solution.

Meanwhile, in relation to the use of such a polarizing plate in a liquidcrystal display (LCD), or the like, a technique of attaching a luminanceenhancement film such as a DBEF film to 3M Company to one surface of thepolarizing film to use the same for the purpose of luminance enhancementhas been proposed. However, when the luminance enhancement film isattached to the related art polarizing plate, a curling phenomenon(referred to as negative directional curling, hereafter), in which acentral surface of the polarizing plate becomes downwardly concave,occurs due to a high shrinkage rate of the luminance enhancement film.If such negative directional curling occurs on the polarizing film, whena liquid crystal panel is mounted on a module of the LCD, a cornerportion of the liquid crystal panel comes off due to the curledpolarizing plate so as to be brought into contact with a case, and as aresult, a great deal of stress is formed at the corner portion to causea corner light leakage phenomenon. Such a corner light leakagephenomenon causes a defective image.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a luminance enhancementfilm-attached polarizing plate capable of improving a corner lightleakage phenomenon by controlling the direction of curling generatedwhen a luminance enhancement film is attached, a fabrication methodthereof, and a display device using the same.

According to an aspect of the present invention, there is provided apolarizing plate including: a polarizing element; a first adhesive layerformed on one surface of the polarizing element; a second adhesive layerformed on the other surface of the polarizing element; a protective filmattached to the first adhesive layer; a bonding layer attached to thesecond adhesive layer; and a luminance enhancement film attached to thebonding layer.

The first and second adhesive layers may be made of the same material,but the present invention is not limited thereto.

The polarizing element may be a polyvinyl alcohol (PVA)-based polarizingfilm in which molecule chains containing an iodine-based compound ordichroic polarizing material are oriented in a certain direction.

The first and second adhesive layers may be made of an adhesive resinincluding one or more types selected from the group consisting of apolyvinyl alcohol (PVA)-based resin, an acrylic resin, avinylacetate-based resin, and a UV-curing resin.

The first and second adhesive layers may be made of an adhesive resinincluding a PVA resin having an acrylic group and a hydroxyl group.

The first and second adhesive layers may be made of an adhesive resinincluding 100 parts by weight of a PVA-based resin and 0.01 to 10 partsby weight of a compound having an epoxy group and an acrylic group.

The adhesive resin may additionally include an initiator configured asan AIBN-based initiator and/or a persulfate-based water-solubleinitiator, and in this case, a maximum 10 wt % of the initiator based onthe weight of the adhesive resin may be added.

The protective film may be made of one or more types selected from thegroup consisting of a polyester-based polymer, a styrene-based polymer,a cellulose-based polymer, a polyethersulfone-based polymer, apolycarbonate-based polymer, an acrylic polymer, a polyolefin-basedpolymer, a polyamide-based polymer, a polyimide-based polymer, asulfone-based polymer, a polyether sulfone-based polymer, a polyetherether ketone-based polymer, a polyphenylene sulfide-based polymer, avinyl alcohol-based polymer, a vinylidene chloride-based polymer, avinyl butyral-based polymer, an arylate-based polymer, apolyoxymethylene-based polymer, an epoxy-based polymer, or any mixturethereof.

The bonding layer may be made of one or more types selected from thegroup consisting of an acrylic copolymer, an epoxy-based resin, apolyurethane-based resin, a silicon-based resin, a polyether-basedresin, a polyamide-based resin, and a PVA-based resin.

The bonding layer may be configured as a single layer, or may includetwo bonding layers, i.e., first and second bonding layers, each having adifferent modulus.

The modulus of the first bonding layer may range from about 1 to 500MPa, the modulus of the second bonding layer may range from about 0.01to 0.5 MPa, and the first bonding layer having a greater modulus valuemay be attached to the second adhesive layer.

The luminance enhancement film may be a multilayer reflective polarizer,a multilayer reflective film, or a nano-wire grid polarizer.

According to another aspect of the present invention, there is provideda method for fabricating a polarizing plate, including: positioning aprotective film on one surface of a polarizing element and positioning abonding layer on the other surface of the polarizing element;interposing an adhesive between the protective film and the polarizingelement and between the bonding layer and the polarizing element;attaching the protective film and the bonding layer to the polarizingelement by the medium of the adhesive and drying the same; and attachinga luminance enhancement film to the bonding layer.

The drying may be performed at 20° C. to 100° C., or may be performed at40° C. to 90° C.

According to another aspect of the present invention, there is provideda display device including the foregoing polarizing plate. The displaydevice may be a liquid crystal display (LCD) or an organicelectroluminescence (EL), and in the case of the LCD, a driving mode maybe an in-plane switching (IPS) mode, a twisted nematic (TN) mode, avertically aligned (VA) mode, or a fringe field switching (FFS) mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a view showing an example of a polarizing plate according toan embodiment of the present invention.

FIG. 2 is a view showing another example of a polarizing plate accordingto an embodiment of the present invention.

FIG. 3 is a view explaining a method for fabricating a polarizing plateaccording to an embodiment of the present invention.

FIG. 4 is a photograph obtained by capturing a polarizing platefabricated according to Embodiment Example of the present invention.

FIG. 5 is a photograph obtained by capturing a polarizing platefabricated according to Comparative Example of the present invention.

FIG. 6 is a photograph of a corner light leakage phenomenon of an IPSmode LCD in which the polarizing plates fabricated according toEmbodiment Example and Comparative Example of the present invention areinstalled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings. The invention may, however,be embodied in many different forms and should not be construed as beinglimited to the embodiments set forth herein. Rather, these embodimentsare provided so that this disclosure will be thorough and complete, andwill fully convey the scope of the invention to those skilled in theart. In the drawings, the shapes and dimensions of elements may beexaggerated, reduced, or omitted for clarity, and the same referencenumerals will be used throughout to designate the same or likecomponents.

FIG. 1 is a view showing an example of a polarizing plate according toan embodiment of the present invention. As shown in FIG. 1, a polarizingplate 1 according to an embodiment of the present invention includes apolarizing element 10, a first adhesive layer 20, a second adhesivelayer 40, a protective film 30, a bonding layer 50, and a luminanceenhancement film 60.

In detail, as shown in FIG. 1, the polarizing plate has a structure inwhich the protective film 30 is attached only to one surface of thepolarizing element 10 and the bonding layer is directly attached to theadhesive layer without a protective film. Research conducted by theinventors of the present application showed that, as in the polarizingplate according to an embodiment of the present invention, in case ofattaching protective film only to one surface of the polarizing element,the polarizing plate can become advantageously thinner and morelightweight and a light leakage phenomenon is significantly improved ascurling occurs in a positive direction, unlike the related art in whichthe luminance enhancement film is attached to the polarizing plate inwhich protective film is attached to both surfaces of the polarizingelement.

The polarizing element 10 refers to an optical element allowing onlylight having a particular polarized state to pass therethrough, forwhich, in general, a PVA-based polarizing film in which molecule chainscontaining an iodine-based compound or dichroic dye are oriented in acertain direction is used. Such a polarizing film is fabricated bydyeing an iodine or dichroic dye on a PVA-based film and stretching thesame in a certain direction, and cross-linking the same. Here, thedegree of polymerization of the PVA is not particularly limited, yet inconsideration of freedom in movement of molecules and flexible mixturewith the containing material, it ranges preferably, from about 1,000 to10,000, and more preferably, from about 1,500 to 5,000.

The first adhesive layer 20, which serves to attach the protective film30 to be described and the polarizing element 10, is formed on onesurface of the polarizing element 10.

Meanwhile, the second adhesive layer 40, which serves to attach thepolarizing element 10 and the bonding layer 50, is formed on a surfaceof the polarizing element 10 on which the first adhesive layer 20 is notformed.

In an embodiment of the present invention, preferably, the firstadhesive layer 20 and the second adhesive layer 40 are made of anadhesive resin of the same material, but the present invention is notlimited thereto. When the adhesive layers made of the same material areformed on both surfaces of the polarizing element 10, since shrinkage ofthe both adhesive layers is identical, the same force is applied to thepolarizing element 10 after drying, and as a result, generation ofcurling due to contraction of the adhesive, or the like, can beminimized.

Meanwhile, the adhesive resin forming the first adhesive layer 20 andthe second adhesive layer 40 is not particularly limited. Namely, anadhesive resin which has excellent optical transmission and is notchanged, such as yellowed, or the like, over time, may be used. Forexample, in an embodiment of the present invention, the first adhesivelayer 20 may be formed by using an adhesive resin including a polyvinylalcohol-based resin, an acrylic resin, a vinyl acetate-based resin,and/or a UV-curing resin, or the like, and in this case, the adhesiveresins may be water-based adhesives or solventless type adhesives.

However, among them, in particular, a water-based adhesive including aPVA-based resin is preferably used, and an adhesive resin including aPVA-based resin (referred to as an ‘AH-PVA resin’, hereinafter) havingacrylic group or a hydroxyl group or an adhesive resin including aPVA-based resin and a compound having an acrylic group and an epoxygroup may be more preferably used. The adhesive resin including theAH-PVA resin or the adhesive resin including the PVA-based resin and acompound having an acrylic group and an epoxy group has advantages inthat it has excellent adhesive strength, water resistance, and moistureresistance as well as having excellent solubility over water.

In detail, the AH-PVA resin used in an embodiment of the presentinvention may include a recurring unit expressed by Chemical Formula 1ashown below and a recurring unit expressed by Chemical Formula 1b shownbelow, and selectively additionally includes a recurring unit expressedby Chemical Formula 1c shown below.

Here, in the above Chemical Formulas, R¹ may be a substituted orunsubstituted C₁-C₂₀ alkandiyl; a substituted or unsubstituted 1 to7-membered cyclic compound; a substituted or unsubstituted 1 to7-membered heterocyclic compound including a hetero atom selected fromthe group consisting of N, S, and O; a substituted or unsubstitutedC₆-C₁₄ aromatic compound; or a substituted or unsubstituted 1 to7-membered hetero aromatic compound including a hetero atom selectedfrom the group consisting of N, S, and O, and R² may be a substituted orunsubstituted C₁-C₂₀ alkyl group; a substituted or unsubstituted 1 to7-membered cyclic compound; a substituted or unsubstituted 1 to7-membered heterocyclic compound including a hetero atom selected fromthe group consisting of N, S, and O; a substituted or unsubstitutedC₆-C₁₄ aromatic compound; or a substituted or unsubstituted 1 to7-membered hetero aromatic compound including a hetero atom selectedfrom the group consisting of N, S, and O. When R¹ and R² are substitutedwith a substituent, the substituent may be a C₁-C₂₀ alkyl group or ahalogen atom selected from the group consisting of F, Cl, Br, and I, andR³ may be an acetoacetyl group, a carboxylic acid group, an acryl group,or a urethane group.

Meanwhile, when the AH-PVA resin includes the recurring unit expressedby Chemical Formula 1a and the recurring unit expressed by Chemicalformula 1b, preferably, n is an integer ranging from 480 to 1700, m isan integer ranging from 10 to 900, and n+m is an integer ranging from500 to 1800. When the AH-PVA resin includes the recurring unit expressedby Chemical Formula 1a, the recurring unit expressed by Chemical Formula1b, and the recurring unit expressed by Chemical Formula 1c, preferably,n is an integer ranging from 480 to 1700, m is an integer ranging from10 to 900, l is an integer ranging from 1 to 80, n+m is an integerranging from 500 to 1800, n+1 is an integer ranging from 490 to 1700,and n+m+l is an integer ranging from 500 to 1800 in the ChemicalFormulas.

Meanwhile, the recurring units expressed by Chemical Formulas 1a, 1b,and 1c may be randomly arranged within the AH-PVA resin polymer.

Meanwhile, in the AH-PVA resin, the acrylic group may be contained to be0.1˜50 mol %, preferably, 0.1˜20 mol %, and more preferably, 0.1˜10 mol% of the PVA resin. If the content of the acrylic group in the PVA resinis less than 0.1 mol %, the effect of increasing adhesiveness, moistureresistance, water resistance according to the inclusion of the acrylicgroup cannot be obtained, and if the content of the acrylic groupexceeds 50 mol %, solubility with respect to water would be degraded andadhesive strength would be reduced.

The AH-PVA resin is obtained by modifying a PVA-based resin with acompound having an epoxy group and an acrylic group. Here, as thecompound having an epoxy group and an acrylic group, the compound ofChemical Formula 3 shown below may be used. R¹ and R² in ChemicalFormula 3 are defined to be the same as that described above.

In detail, the AH-PVA resin according to an embodiment of the presentinvention may be prepared by the following Reaction Formula 1.

Reaction Formula 1 expresses the process of being changed the relatedart PVA-based resin into the AH-PVA resin and the number of recurringunits is not mentioned. In Reaction Formula 1, Chemical Formula 2 is aPVA-based resin. The PVA-based resin used in an embodiment of thepresent invention is not particularly limited and an arbitrary PVA-basedresin, e.g., a non-modified PVA resin, a PVA resin modified by at leastone type of group selected from the group consisting of an acetoacetylgroup, a carboxylic acid group, an acrylic group, and a urethane group,or the like, known in the art to be used in an adhesive for attachingthe polarizing element and the protective film in the related art, maybe used. When a non-modified PVA-based resin is used as the PVA resin,the recurring unit 1c in Chemical Formula 2 may not exist.

As expressed by Reaction Formula 1, in the reaction of the PVA inChemical Formula 2 and the compound having the epoxy group and the acrylgroup in Chemical Formula 3, as the hydroxyl group (—OH) and/or R³ groupof PVA are reacted to the epoxy group, the acrylic group is introducedinto the PVA resin and the hydroxyl group (—OH) is formedsimultaneously.

In detail, as expressed by Reaction Formula 1, when the PVA resin(Chemical Formula 2) and the compound having the epoxy group and theacrylic group (Chemical Formula 3) are dissolved in water and reacted atabout 25 to 70 for 10 to 30 hours, the PVA-based resin (ChemicalFormula 1) in which the acrylic group has been introduced and the —OHgroup has been formed can be obtained. Namely, according to theforegoing reaction, the PVA resin in which the acrylic group has beenintroduced to a backbone of the resin and the —OH group has been formedis obtained, and the PVA-based resin with the acrylic resin introducedinto the backbone thereof and —OH group formed therein has excellentwater solubility, adhesiveness, water resistance, and moistureresistance.

Meanwhile, preferably, a copolymerization degree of the AH-PVA resinranges from about 500 to 1800. If the copolymerization degree is lessthan 500, when an adhesive is prepared, viscosity would be low at a lowsolid content, so a great amount of solid content should be added. Ifthe copolymerization degree exceeds 1800, when an adhesive is prepared,viscosity would be high, so a small amount of solid content(PVA resin)should be added, and in this case, adhesive strength would be reduced,which is, thus, not desirable.

Meanwhile, as a material for forming the first adhesive layer and thesecond adhesive layer according to an embodiment of the presentinvention, an adhesive resin including a PVA-based resin and a compoundhaving an epoxy group and an acrylic group may be used instead of theAH-PVA resin.

In the adhesive resin, the content of the compound having an epoxy groupand an acrylic group is 0.001 to 10 parts by weight, preferably, 0.001to 1 parts by weight over 100 parts by weight of the PVA-based resin.

Meanwhile, the PVA-based resin used in the adhesive resin including aPVA resin and a compound having an epoxy group and an acrylic group isalso not particularly limited and an arbitrary PVA-based resin known inthe art, e.g., a non-modified PVA resin, a PVA resin modified by atleast one type of group selected from the group consisting of anacetoacetyl group, a carboxylic acid group, an acrylic group, and aurethane group, or the like, may be used.

Here, preferably, a copolymerization degree of the PVA-based resinranges from about 500 to 1800. If the copolymerization degree is lessthan 500, when an adhesive is prepared, viscosity would be low at a lowsolid content, so a great amount of solid content should be added. Ifthe copolymerization degree exceeds 1800, when an adhesive is prepared,viscosity would be high, so a small amount of solid content(PVA resin)should be added, and in this case, adhesive strength would be reduced,which is, thus, not desirous.

As the compound having an epoxy group and an acrylic group, the compoundof Chemical Formula 3 may be used. If the content of the compound havingan epoxy group and an acrylic group is less than 0.001 parts by weight,the effect of increasing adhesiveness, moisture resistance, and waterresistance according to the inclusion of the acrylic group could not beobtained, and if the content of the compound having an epoxy group andan acrylic group exceeds 10 parts by weight, water solubility would betoo low to obtain a uniform adhesive to be used for a polarizing plate,and because solution stability and adhesive strength thereof aredegraded, it is not desirous.

Meanwhile, a curing initiator may be added additionally to the adhesiveresin used in an embodiment of the present invention as necessary. Asthe curing initiator, an AIBN(2,2′-azo-bis(isobutyronitrile))-basedinitiator, a persulfate-based initiator, an initiator of Darocure and/orIgacure series to Ciba-Geigy Ltd., or the like, may be used. The AIBNand persulfate-based initiators may be used based on water, and anyinitiator known in the art may be used. The AIBN-based initiator mayinclude, for example, 2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(2-imidazolin -2-yl)propane]disulfate dihydrate,2,2′-azobis[N-(2-carboxyethyl)-2-methylpropionamide],2,2′-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochloride,2,2′-azobis{2-[1-(2-hydroxyethyl)-2-yl] propane}dihydrochloride, 2,2′-azobis {2-methyl-N-[2-(hydroxybutyl)] propionamide}, 2,2′- azobis[2-methyl-N-[2-(hydroxyethyl)propionamide], 2,2′- azobis(N-butyl-2-methylpropionamide), and the like, and as thepersulfate-based curing initiator may include, for example, potassiumpersulfate, ammonium persulfate, and the like, but the present inventionis not limited thereto. The initiators to Ciba-Geigy Ltd. may include,for example,hydroxy-1-[4-(hydroxyethoxy)phenol]-2-methyl-1-propanone(Darocure 2959),2-hydroxy-2-methyl-1-phenylpropan-1-one(Darocure 1173),1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one(Darocure 1116),25:75 blend of bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide and 2-hydroxy-2-methyl-1-phenylpropan-1-one (Brand name:Irgacure 1700),1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one(Irgacure2959), 1-hydroxycyclohexylphenylketone (Irgacure 184),2,2-dimethoxy-2-phenylacetophenone(Irgacure 651), and the like, but thepresent invention is not limited thereto.

The curing initiator may be added to be a maximum 10 wt % based on thetotal weight of the adhesive resin. The curing initiator is a componentarbitrarily added as necessary. Although a lower limit value of theadded amount is not limited, preferably, the curing initiator may beadded to be preferably 0.01 to 10 wt %, and more preferably, 0.01 to 1wt % based on the total weight of the adhesive. If the added amount ofthe curing initiator is less than 0.01 wt %, the effect of adding thecuring initiator is insufficient, and when the added amount of thecuring exceeds 10 wt %, the additive remaining after the reaction wouldmake a bad influence on the adhesive strength, and thus, not desirous.

Besides, in the adhesive resin, various coupling agents, tackifiers, UVray absorbents, antioxidants, various stabilizers, and the like, may becombined as necessary.

Next, the protective film 30, a film for protecting the polarizingelement 10, is attached to an upper portion of the first adhesive layer20. As the protective film 30, any polymeric films having excellentoptical transparency, mechanical strength, thermal stability, isotropy,adhesive property with a PVA polarizing element, and the like, may beused. For example, a film made of a polyester-based polymer such aspolyethylene terephthalate, polyethylene naphthalate, and the like, astyrene-based polymer such as polystyrene, a copolymer of acrylonitrileand styrene, and the like, a cellulose-based polymer such as diacetylcellulose, triacetyl cellulose, and the like, a polyethersulfone-basedpolymer, a polycarbonate-based polymer, an acrylic polymer such aspolyemthylmethacrylate, and the like, a polyolefin-based polymer such aspolyethylene, polypropylene, and a copolymer of ethylene and propylene,an amide-based polymer such as nylon or aromatic polyamide, animide-based polymer, a sulfone-based polymer, a polyether sulfone-basedpolymer, a polyether ether ketone-based polymer, a polyphenylenesulfide-based polymer, a vinyl alcohol-based polymer, a vinylidenechloride-based polymer, a vinyl butyral-based polymer, an arylate-basedpolymer, a polyoxymethylene-based polymer, an epoxy-based polymer, orany mixture thereof may be used as the protective film, but the presentinvention is not limited thereto.

In particular, a cellulose-based film such as a film of cellulose ester,triacetyl cellulose (TAC), a film of cellulose propionate, celluloseacetate propionate, cellulose diacetate, cellulose acetate butylate, andthe like, a polycarbonate-based film (PC film), a polystyrene-basedfilm, a polyarylate-based film, a norbornene resin-based film, and apolysulfone-based film are preferable in the aspect that they aretransparent, have mechanical properties, do not have optical anisotropy,and the like. The triacetyl cellulose film (TAC film) and thepolycarbonate film (PC film) are more preferable in that they haveexcellent film forming properties and processibility. The TAC film ismost preferable due to its polarization characteristics and durability.

The protective film may be surface-modified in order to have improvedadhesive strength and adhesion with respect to the polarizing element towhich the protective film is attached. The surface treatment mayinclude, for example, a corona treatment, a glow discharge treatment, aflame treatment, acidification, an alkali treatment, a plasma treatment,ultrasonication, UV irradiation, and the like, but the present inventionis not limited thereto. Also, in order to enhance adhesive properties, amethod of providing an undercoat layer to the protective film may alsobe used.

The bonding layer 50, which serves to attach the luminance enhancementfilm 60, is attached to a lower portion of the second adhesive layer 40.As a material of the bonding layer 50, for example, an acryliccopolymer, an epoxy resin, a polyurethane resin, a silicon resin, apolyether resin, a polyamide resin, a polyvinylalcohol resin, and thelike, may be used alone or may be mixed together so as to be used. Amongthem, in particular, the acrylic copolymer is preferably used inconsideration of transparency, weatherproof, durability, and adhesionproperties, and the like.

Meanwhile, the bonding layer 50 may have a mono-layer structure as shownin FIG. 1 or may include a first bonding layer 50 a and a second bondinglayer 50 b each having a different modulus as shown in FIG. 2. Here,modulus, a measure indicating elastic characteristics of an arbitrarymaterial, is defined as a proportional coefficient between stress andstrain with respect to an arbitrary spatial position and time within amaterial. Namely, in case of simple tension, when stress is σ, strain isε, and modulus is E, it may be defined such that σ=E·ε.

When the bonding layer is formed to have a dual-layer structure, modulusof the first bonding layer may be controlled to be greater than that ofthe second bonding layer to enhance the protection function of the PVApolarizing element. In other words, the bonding layer having dual-layerstructure may have a function of protecting the PVA polarizing elementagainst external environmental factors, such as heat, moisture, or thelike, that degrade the polarization function of the PVA polarizingelement. Also, a chemical functional group may be added to a gluingagent forming the first bonding layer to improve adhesive strength withrespect to the PVA polarizing element and water resistance.

In this case, modulus of the first bonding layer ranges from about 1 to500 MPa, preferably, ranges from about 50 to 450 MPa, and morepreferably, ranges from about 100 to 400 MPa, and modulus of the secondbonding layer ranges from about 0.01 to 0.5 MPa, preferably, ranges fromabout 0.01 to 0.45 MPa, and more preferably, ranges from about 0.01 to0.4 MPa.

As shown in FIG. 2, when the bonding layer is formed as two layers eachhaving a different modulus, preferably, a bonding layer having a highermodulus value is attached to the second adhesive layer. The bondinglayer having a higher modulus is able to enhance adhesive strength withrespect to the PVA polarizing element and increase water resistance ofthe polarizing plate by improving wettability of the second adhesivelayer, as well as effectively protecting the PVA polarizing elementagainst external environmental factors such as heat, moisture, or thelike. Meanwhile, the bonding layer having a low modulus value may beused to be bonded with the luminance enhancement film.

As the luminance enhancement film 60, general films used to enhanceluminance of the display device in the art may be used withoutlimitation. For example, in an embodiment of the present invention, amultilayer reflective polarizer such as a DBEF film manufactured andpurchased by 3M, a multilayer reflective film in which a plurality oflayers, composed of materials each having a different refractive index,are sequentially laminated, a nano-wire grid polarizer, or the like, maybe used as the luminance enhancement film 60.

Here, the multilayer reflective film may have a structure in which onelayer has an isotropic structure, another layer has an anisotropicstructure, and layers whose refractive index in one direction is greaterthan refractive index of an isotropic layer are sequentially laminated.Namely, on the assumption that two layers, i.e., first and secondlayers, exist, when planar refractive indices in two direction on thefirst layer are n_(x1) and n_(y1), respectively, the first layer isn_(x1)≈n_(y1), and when planar refractive indices of the second layerare n_(x2) and n_(y2), respectively, the second layer is n_(y2)>n_(x2),and a relationship of n_(y2)>n_(x2)≈n_(x1)n_(y1) may be established.

Also, the nano-wire grid polarizer may have a configuration in which anano-structure is formed on a transparent film. Here, the nano-structuremay be a metal layer or may have a configuration in which a metal layeris formed on a resin pattern.

The results of research conducted by the inventors of the presentapplication show that the use of the DBEF film to 3M as the luminanceenhancement film 60 of the present invention attains a luminanceenhancement effect of 40% or more.

A method for fabricating a polarizing plate according to an embodimentof the present invention will be described.

FIG. 3 is a view explaining a method for fabricating a polarizing plateaccording to an embodiment of the present invention. As shown in FIG. 3,the method for fabricating a polarizing plate according to an embodimentof the present invention includes (i) positioning a protective film onone surface of a polarizing element and positioning a bonding layer onthe other surface of the polarizing element, (ii) interposing anadhesive between the protective film and the polarizing element andbetween the bonding layer and the polarizing element, (iii) attachingthe protective film and the bonding layer to the polarizing element bythe medium of the adhesive and drying the same, and (iv) attaching aluminance enhancement film to the bonding layer.

First, the protective film 30 and the bonding layer 50 are positioned onboth sides of the polarizing element 10. In this case, as mentionedabove, preferably, the polarizing element 10 is a PVA polarizing film inwhich molecule chains containing an iodine-based compound or dichroicdye are oriented in a certain direction, and a polymerization degree ofthe PVA ranges from about 1,000 to 10,000, preferably, ranges from about1,500 to 5,000.

Also, as the protective film, a film made of a polyester-based polymersuch as polyethylene terephthalate, polyethylene naphthalate, and thelike, a styrene-based polymer such as polystyrene, a copolymer ofacrylonitrile and styrene, and the like, a cellulose-based polymer suchas diacetyl cellulose, triacetyl cellulose, and the like, apolyethersulfone-based polymer, a polycarbonate-based polymer, anacrylic polymer such as polyemthylmethacrylate, and the like, apolyolefin-based polymer such as polyethylene, polypropylene, and acopolymer of ethylene and propylene, an amide-based polymer such asnylon or aromatic polyamide, an imide-based polymer, a sulfone-basedpolymer, a polyether sulfone-based polymer, a polyether etherketone-based polymer, a polyphenylene sulfide-based polymer, a vinylalcohol-based polymer, a vinylidene chloride-based polymer, a vinylbutyral-based polymer, an arylate-based polymer, apolyoxymethylene-based polymer, an epoxy-based polymer, or any mixturethereof may be used.

Meanwhile, the bonding layer 50 may be optically transparent and exhibitappropriate viscoelasticity or adhesive properties. A material of theboning layer 50 is not particularly limited. For example, as a materialof the bonding layer 50, an acrylic copolymer, an epoxy resin, apolyurethane resin, a silicon resin, a polyether resin, a polyamideresin, a polyvinylalcohol resin, and the like, may be used alone or maybe mixed together so as to be used. Among them, in particular, theacrylic copolymer is preferably used in consideration of transparency,weatherproof, durability, and adhesion properties, and the like.

Here, as the bonding layer 50, an adhesive sheet formed by coating agluing agent on a release film may be used. Here, the adhesive sheet maybe fabricated by applying an adhesive resin on a release film and curingthe same through a method such as drying, thermal curing, chemicalcuring, heat fusion, or light curing.

Also, the bonding layer 50 may include the first bonding layer 50 a andthe second bonding layer 50 b each having a different modulus. In thiscase, modulus of the first bonding layer ranges from about 1 to 500 MPa,preferably, ranges from about 50 to 450 MPa, and more preferably, rangesfrom about 100 to 400 MPa, and modulus of the second bonding layerranges from about 0.01 to 0.5 MPa, preferably, ranges from about 0.01 to0.45 MPa, and more preferably, ranges from about 0.01 to 0.4 MPa.

Next, an adhesive is interposed between the protective film and thepolarizing element and between the bonding layer and the polarizingelement. In this step, as shown in FIG. 3, the adhesive may be appliedto both surfaces of the polarizing element or may be applied to onesurface of the protective film and that of the bonding layer facing thepolarizing element.

Meanwhile, as mentioned above, the adhesive which has adhesive strengthsufficient for attaching the polarizing element and the protective filmor attaching the polarizing element and the bonding layer, has excellentoptical transmission and is not changed, such as yellowed, or the like,over time, may be used, without being particularly limited. For example,an adhesive including one or more types selected from the groupconsisting of a PVA-based resin, an acrylic resin, a vinyl acetate-basedresin, an a UV curing adhesive resin may be used. Preferably, anadhesive including a PVA-based resin is used, and most preferably, anadhesive including a PVA-based resin containing an acrylic group and anhydroxyl group is used.

When the adhesive is interposed through the foregoing process, theprotective film and the bonding layer are attached to the polarizingelement by the medium of the adhesive and dried.

Here, a drying temperature may be generally 20 to 100, more preferably,40 to 90, but it may differ according to an adhesive in use.

Also, if a foreign object exists in attaching the protective film andthe bonding layer to the polarizing element and drying the same, theattachment may not be smoothly performed. Thus, preferably, this step isperformed in an environment in which a floating foreign object is low ora foreign object removal process may be performed before the attachmentstep. As the method for removing a foreign object, any method that maynot make a bad influence on the polarizing element, the protective film,and the bonding layer may be employed without being particularlylimited. For example, in order to remove a foreign object, a cleansingsection may be additionally performed during the polarization platefabrication process to wash out a foreign object from the surface of thefilms in a cleansing tub filled with water. Alternatively, a method ofsloping a film proceeding direction during the process and applyingwater to flow down on the sloped surface to thus remove a foreignobject, a method of cleansing the film and then removing water remainingon the surface of the film by jetting air pressure such as oxygen,nitrogen, or the like, a method for directly jetting air pressure toblow a foreign object to remove it, or the like, may be used.

Meanwhile, in order to perform smooth attachment, preferably, the amountof foreign objects on the contact surface is 1 g/m² or less per unitarea, and more preferably, 0.5 g/m² or less. Here, the amount of foreignobjects refers to weight of foreign objects present per unit surfacearea.

When drying is completed, the luminance enhancement film 60 is attachedto the bonding layer.

Through the foregoing fabrication method, the polarizing plate accordingto an embodiment of the present invention in which the protective film,the first adhesive layer, the polarizing element, the second adhesivelayer, the bonding layer, and the luminance enhancement film aredisposed sequentially from above may be fabricated. Unlike the relatedart luminance enhancement film-attached polarizing plate, in thepolarizing plate according to an embodiment of the present inventionfabricated through the foregoing method, since a central surface of thepolarizing plate is upwardly convex, generating curling in a positivedirection, after the luminance enhancement film is attached, a cornerlight leakage phenomenon can be improved. Also, since only one sheet ofprotective film is used, the polarizing plate can become thinner andmore lightweight.

In addition, when the first and second adhesive layers are made of theAH-PVA resin or the adhesive resin including the PVA resin and thecompound having an acrylic group and an epoxy group, the adhesivestrength, moisture resistance, water resistance, and the like, of thepolarizing plate can be enhanced.

Meanwhile, the polarizing plate according to an embodiment of thepresent invention may be advantageously used as a polarizing plate of adisplay device, e.g., as a polarizing plate of an LCD, as ananti-reflective polarizing plate of an organic EL, or the like. Here,the LCD may be used in various driving modes, for example, an in-planeswitching (IPS) mode, a twisted nematic (TN) mode, a vertically aligned(VA) mode, or a fringe field switching (FFS) mode, and the like, withouta limitation.

Hereafter, the present invention will be described in more detailthrough specific embodiments. However, of course, the scope of thepresent invention is not confined or limited to the followingembodiments.

EMBODIMENT EXAMPLE

A PVA film (manufactured by Kurary Co. Ltd., polymerization degree:2400)was processed in a rinsing tank and a swelling tank, dyed in an aqueoussolution containing I₂ and KI, and then, stretched five-fold in anaqueous solution containing boron and Kl to obtain a polarizer.

And then, a TAC film having a thickness of 60 micrometers was positionedon one surface of the polarizer and a bonding film protected by a PErelease film was positioned on the other surface of the polarizer. Here,the bonding film was configured as a bonding layer including two layershaving modulus values of 270 MPa and 0.02 MPa, respectively.

Thereafter, a PVA-based adhesive aqueous solution was put between thepolarizer and the TAC film and between the polarizer and the bondingfilm, attached together by laminator, and then, dried for 8 minutes at80. And then, the DBEF film to 3M was attached to the bonding film tofabricate the polarizing plate having such a structure as shown in FIG.2.

COMPARATIVE EXAMPLE

For comparison, a bonding layer having a modulus value of 0.02 MPa wasformed on one surface of the related art polarizing plate in which aPVA-based adhesive layer and a TAC film were sequentially laminated onboth surfaces of the same PVA film as that of the Embodiment Example,and the DBEF film to 3M was attached to the bonding layer.

EXPERIMENTAL EXAMPLE 1

Curling generation degrees of the polarizing plates fabricated accordingto Embodiment Example and Comparative Example were measured throughnaked eyes. FIG. 4 is a photograph obtained by capturing the polarizingplate fabricated according to Embodiment Example of the presentinvention. FIG. 5 is a photograph obtained by capturing a polarizingplate fabricated according to Comparative Example. In this case, therespective polarizing plates were placed such that the surfaces thereofto which the luminance enhancement film was attached faced downward.

As shown in FIGS. 4 and 5, it can be seen that, in the case of thepolarizing plate according to Comparative Example, the corner portion ofthe polarizing plate faces in an upward direction, generating negativecurling, while in the case of the polarizing plate according toEmbodiment Example, the corner portion of the polarizing plate faces ina downward direction, generating positive curling.

EXPERIMENTAL EXAMPLE 2

The polarizing plates fabricated according to Embodiment Example andComparative Example were mounted in an 17-inch IPS mode LCD monitor anda light leakage phenomenon was observed. FIG. 6 is photograph obtainedby capturing the monitor with the polarizing plate according toEmbodiment Example attached thereto and the monitor with the polarizingplate according to Comparative Example attached thereto.

As shown in FIG. 6, it can be seen that the corner light leakagephenomenon was significantly reduced when the polarizing plate accordingto Embodiment Example was mounted.

As set forth above, unlike the related art luminance enhancementfilm-attached polarizing plate, in the luminance enhancementfilm-attached polarizing plate according to an embodiment of the presentinvention, since a central surface of the polarizing plate is upwardlyconvex, generating curling in a positive direction, after the luminanceenhancement film is attached, a corner light leakage phenomenon can beimproved. Also, since only one sheet of protective film is used, thepolarizing plate can become thinner and more lightweight.

In addition, since the adhesive resin including a PVA resin having anacrylic group and the hydroxyl group is used as an adhesive of thepolarizing plate according to an embodiment of the present invention,durability and water resistance of the polarizing plate can be enhanced.

While the present invention has been shown and described in connectionwith the embodiments, it will be apparent to those skilled in the artthat modifications and variations can be made without departing from thespirit and scope of the invention as defined by the appended claims.

1. A polarizing plate comprising: a polarizing element; a first adhesivelayer formed on one surface of the polarizing element; a second adhesivelayer formed on the other surface of the polarizing element; aprotective film attached to the first adhesive layer; a bonding layerattached to the second adhesive layer; and a luminance enhancement filmattached to the bonding layer.
 2. The polarizing plate of claim 1,wherein the first adhesive layer and the second adhesive layer are madeof an adhesive resin including one or more types selected from the groupconsisting of a PVA-based resin, an acrylic resin, a vinylacetate-basedresin, and a UV-curing resin and are made of the same material.
 3. Thepolarizing plate of claim 2, wherein the first adhesive layer and thesecond adhesive layer are made of an adhesive resin including a PVAresin having an acrylic group and a hydroxyl group.
 4. The polarizingplate of claim 3, wherein the PVA resin having an acrylic group and ahydroxyl group includes recurring units expressed by Chemical Formula 1ashown below and recurring units expressed by Chemical Formula 1b shownbelow:

wherein n is an integer ranging from 480 to 1700, m is an integerranging from 10 to 900, and n+m is an integer ranging from 500 to 1800,R^(l) is a substituted or unsubstituted C_(l)-C₂₀ alkandiyl; asubstituted or unsubstituted 1 to 7-membered cyclic compound; asubstituted or unsubstituted 1 to 7-membered heterocyclic compoundincluding a hetero atom selected from the group consisting of N, S, andO; a substituted or unsubstituted C₆-C₁₄ aromatic compound; or asubstituted or unsubstituted 1 to 7-membered hetero aromatic compoundincluding a hetero atom selected from the group consisting of N, S, andO, and R² is a substituted or unsubstituted C₁-C₂₀ alkyl group; asubstituted or unsubstituted 1 to 7-membered cyclic compound; asubstituted or unsubstituted 1 to 7-membered heterocyclic compoundincluding a hetero atom selected from the group consisting of N, S, andO; a substituted or unsubstituted C₆-C₁₄ aromatic compound; or asubstituted or unsubstituted 1 to 7-membered hetero aromatic compoundincluding a hetero atom selected from the group consisting of N, S, andO, and when R¹ and R² are substituted with a substituent, thesubstituent is a C₁-C₂₀ alkyl group or a halogen atom selected from thegroup consisting of F, Cl, Br, and I.
 5. The polarizing plate of claim3, wherein the PVA resin having an acrylic group and a hydroxyl groupfurther includes recurring units expressed by Chemical Formula 1c shownbelow

wherein n is an integer ranging from 480 to 1700, m is an integerranging from 10 to 900, l is an integer ranging from 1 to 80, n+m is aninteger ranging from 500 to 1800, n+1 is an integer ranging from 490 to1700, and n+m+l is an integer ranging from 500 to 1800, and R³ is anacetoacetyl group, a carboxylic acid group, an acryl group, or aurethane group.
 6. The polarizing plate of claim 3, wherein the adhesiveresin additionally includes an initiator configured as an AIBN-basedinitiator or a persulfate-based water-soluble initiator.
 7. Thepolarizing plate of claim 6, wherein a maximum 10 wt % of the initiatorbased on the weight of the adhesive resin is added.
 8. The polarizingplate of claim 2, wherein the first adhesive layer and the secondadhesive layer are made of an adhesive resin including 100 parts byweight of a PVA resin and 0.01 to 10 parts by weight of a compoundhaving an epoxy group and an acrylic group.
 9. The polarizing plate ofclaim 8, wherein the compound having an epoxy group and an acryl groupis a compound expressed by Chemical Formula 3 shown below: [ChemicalFormula 3]

wherein R¹ is a substituted or unsubstituted C₁-C₂₀ alkandiyl; asubstituted or unsubstituted 1 to 7-membered cyclic compound; asubstituted or unsubstituted 1 to 7-membered heterocyclic compoundincluding a hetero atom selected from the group consisting of N, S, andO; a substituted or unsubstituted C₆-C₁₄ aromatic compound; or asubstituted or unsubstituted 1 to 7-membered hetero aromatic compoundincluding a hetero atom selected from the group consisting of N, S, andO, and R² is a substituted or unsubstituted C₁-C₂₀ alkyl group; asubstituted or unsubstituted 1 to 7-membered cyclic compound; asubstituted or unsubstituted 1 to 7-membered heterocyclic compoundincluding a hetero atom selected from the group consisting of N, S, andO; a substituted or unsubstituted C₆-C₁₄ aromatic compound; or asubstituted or unsubstituted 1 to 7-membered hetero aromatic compoundincluding a hetero atom selected from the group consisting of N, S, andO, and when R¹ and R² are substituted with a substituent, thesubstituent is a C₁-C₂₀ alkyl group or a halogen atom selected from thegroup consisting of F, Cl, Br, and I.
 10. The polarizing plate of claim8, wherein the PVA resin has a polymerization degree ranging from about500 to
 1800. 11. The polarizing plate of claim 8, wherein the adhesiveresin additionally includes an initiator configured as an AIBN-basedinitiator or a persulfate-based water-soluble initiator.
 12. Thepolarizing plate of claim 11, wherein a maximum 10 wt % of the initiatorbased on the weight of the adhesive resin is added.
 13. The polarizingplate of claim 1, wherein the bonding layer includes first bonding layerand second bonding layer, each having a different modulus.
 14. Thepolarizing plate of claim 13, wherein the modulus of the first bondinglayer ranges from about 1 to 500 MPa, and the modulus of the secondbonding layer ranges from about 0.01 to 0.5 MPa.
 15. The polarizingplate of claim 13, wherein the first bonding layer is attached to thesecond adhesive layer.
 16. The polarizing plate of claim 1, wherein theluminance enhancement film is a multilayer reflective polarizer.
 17. Thepolarizing plate of claim 1, wherein the luminance enhancement film is anano-wire grid polarizer including a transparent film, a nano-structureformed on one surface of the transparent film, and a metal layer formedon the nano-structure.
 18. A display device comprising the polarizingplate of claim
 1. 19. A method for fabricating a polarizing plate, themethod comprising: positioning a protective film on one surface of apolarizing element and positioning a bonding layer on the other surfaceof the polarizing element; interposing an adhesive between theprotective film and the polarizing element and between the bonding layerand the polarizing element; attaching the protective film and thebonding layer to the polarizing element by the medium of the adhesiveand drying the same; and attaching a luminance enhancement film to thebonding layer.
 20. The method of claim 19, wherein the drying isperformed at 20° C. to 100° C.